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CV Perf Tech II > Hypothermia- Exam 1 > Flashcards

Hypothermia- Exam 1 Flashcards

1
Q

What is the hypothalamus responsible for?

A 
Vascular regulation (vasoconstriction of skin vessels in cold)
Skeletal Muscle activity (vasodilation of skeletal muscle vascular beds in cold)
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2
Q

What does the endocrine system do?

A

Metabolic regulation

Stress response

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3
Q

What system does hypothermia activate?

A

Endocrine system

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4
Q

Hypothalamus triggers ___________ nervous system response (triggered by the cold).

A

Sympathetic

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5
Q

Cold is sensed by what in the skin?

A

Thermoreceptors

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6
Q

What does activation of the endocrine system result in?

A

Oxygen consumption increases
HR increases
CO increases
BP increases

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7
Q

What temperature is mild hypothermia?

A

32-35 C

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8
Q

What temperature is moderate hypothermia?

A

28-31 C

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9
Q

What temperature is deep hypothermia?

A

18-27 C

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10
Q

What temperature is profound hypothermia?

A

< 18 C

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11
Q

Why induce hypothermia?

A

During bypass it provides degree of orange and organism protection; margin of safety

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12
Q

3 Mechanisms of Protection in hypothermia

A
  1. Reduction in metabolic rate and O2 Consumption
  2. Preservation of high-energy phosphate stores
  3. Reduction of excitatory neurotransmitters release due to ischemia
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13
Q

What happens with glutamate during ischemia?

A

It accumulates, opens calcium channels and activates multiple destructive enzymatic systems

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14
Q

Which is longer: safe period of hypothermia CPB or period predicted on the basis of reduced metabolic activity alone?

A

Safe period of hypothermia CPB

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15
Q

What are the general effects of hypothermia?

A

Allows lower pump flows
Better myocardial protection
less blood trauma (low flow = low damage)
Better overall organ protection

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16
Q

What is the cardiac index for 34-37 C?

A

2.4 L/min/m2

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17
Q

What is the cardiac index for 30-34 C?

A

2.0 L/min/m2

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18
Q

What is the cardiac index for 25-30 C?

A

1.8 L/min/m2

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19
Q

What is the cardiac index for 20-18 C?

A

1.5 L/min/m2

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20
Q

What is the cardiac index for 18 C?

A

1.0 L/min/m2

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21
Q

Methods of Hypothermia Induction

A 
Surface cooling (ice)
Surface cooling w. supplementary partial bypass
Core cooling - Total ECC (DHCA, HLFB, HILFB)
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22
Q

How is surface cooling related to size?

A

Inverse effect related to size; small infants less than 5kg

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23
Q

When do you use DHCA?

A

Complex congenital heart defects
operations on the aortic arch
operations where maintenance of venous drainage is difficult

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24
Q

What should you do if the arrest period is longer than 60 minutes?

A

use intermittent arrest with brief periods of hypothermic flow
low-flow hypothermic perfusion is safer than total arrest

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25
Q

What are the basic global effects of hypothermia?

A

Decreased energy
More bleeding
diminished neuro transmission, receptor function, and protein activity

26
Q

Q10 Principle

A

relates an increase or decrease in reaction rates to a change in 10 C

If Q10=2, a decrease in temperature 10C will result in 50% reduction in reaction rates

27
Q

What is the Q10 value for most physiological rates?

A

2-3

28
Q

Q10 Range (humans)

A 
1.9-4.2 (mean=2)
Organ/tissue variability
temperature variability (2.23 at 27-30C)
4.5 at 14-27C
29
Q

7 degree C Principle

A

Every 7C drop in temperature will result in a 50% decrease in oxygen consumption (and demand)

30
Q

How do the levels of hypothermia relate to decrease in oxygen consumption?

A

Mild: 25% decrease
Moderate: 50 % decrease
Deep: 75% decrease
Profound: 87.5 % decrease

31
Q

At 30C VO2 is what percent of normal?

A

50% normal

32
Q

At 23C VO2 is what percent of normal?

A

25% normal

33
Q

What does pH respond to?

A

Changes in CO2 content, not changes in the CO2 components

34
Q

What does temperature change? (CO2 content or proportion of contents?)

A

Does not change O2 or CO2 content; just the proprotion of the components (dissolved vs partial pressure)

35
Q

Gas solubility is ______________ related to temperature.

A

Inversely

36
Q

Equation for gas content in solution

A

Gas content in solution = pp of gas x solubility

37
Q

Henry’s Law

A

As pressure increases, solubility of gases in liquids increases

As temperature increases, solubility of gases in liquids decreases

38
Q

Temperature is _________ related to partial pressure.

A

Directly

39
Q

Temperature is __________ related to solubility.

A

Inversely

40
Q

Increased temperature ->_________solubility–> _______ partial pressure

A

decreased, increased

41
Q

decreased temperature–> __________ solubility –> _______ partial pressure

A

increased, decreased

42
Q

Recommended rate for cooling?

A

1C per min

43
Q

Recommended rate for warming?

A

1C per 3-5 minutes

44
Q

Consequences on warming too fast

A

development of temp gradients within tissues
body cooling after bypass
exposure to hyperthermia

45
Q

What are the limitations of rate of cooling/warming?

A

Water temp of heat exchanger
BP and SVR
Flow Rate

46
Q

Which temperature gradients do we have to worry about?

A

Btw heat exchanger and venous blood

btw arterial blood and patient

47
Q

Temperature gradients for adults and peds

A

Adults: < 10 C
Peds: < 8 C

48
Q

Keep arterial pO2 below what?

A

<200mmHg

49
Q

What could cause hyperthermia?

A

Time pressure of rewarming
Efficiency of heat exchanger (more or less than expected)
High water temperatures
Perfusionist inattention

50
Q

DHCA Temperature

A

18-20C

51
Q

How long do we turn off the pump in DHCA?

A

30-60 minutes

52
Q

What organ is at greatest risk in DHCA?

A

overall brain function, developmental capacity & IQ

53
Q

What is the safe arrest time for normothermia?

A

4-5 min

O2 consumption 100%

54
Q

What is the safe arrest time for Moderate hypothermia?

A

8-10 min

O2 consumption 50%

55
Q

What is the safe arrest time for deep hypothermia?

A

16-20 min

O2 consumption 25%

56
Q

What is the safe arrest time for profound hypothermia?

A

32-40 min

o2 consumption 12%

57
Q

DHCA Pro’s

A

Allows exposure
reduces metabolic rate and molecule movement
cessation of circulation
excitatory neurotransmitter reduction

58
Q

DHCA Con’s

A

Neurologic Injury & morbidity
BRain is at the most risk
>60 min is detrimental
>40 min increases risk

59
Q

How would you do a combined approach? (HLFB and HILFB)

A

DHCA with intermittent low flow bypass for 1-2 minutes every 15-20 minutes

60
Q

How do you increase tolerance of brain to ischemic result?

A

Thiopental - short acting barbituate

Solumedrol- anti-inflammatory, stabilize cell membranes

61
Q

What is a short acting baribituate to increase tolerance of brain to ischemic insult?

A

Thiopental

62
Q

What is an anti-inflammatory that stabilizes cell membranes to incresa etolerance of brain to ischemic insult?

A

Solumedrol

CV Perf Tech II (17 decks)

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